Abstract

We model the transverse mode interaction in a large-mode-area fiber amplifier by solving the Fresnel wave equation including local gain saturation. In order to calculate the electric field distribution we apply a finite difference beam propagation method, which is followed by the derivation of the modal powers and modal polarization states. A polarization dependent mode amplification is found that is in good agreement with recent experimental results.

Propagation of two modes: (a) gain (shown in linear scale) over propagation distance, (b) intensity distribution within the fiber (normalized for each slice), (c) relative modal powers in modes for p- and s- polarizations, (d) modal polarizations illustrated on the Poincaré sphere (the circles correspond to the initial conditions).

For the case that three modes propagate we calculated the spherical distances between: LP01 and LP11 (d1), LP01 and LP1′1 (d2), LP11 and LP1′1 (d3), and the sum of all distances (d4=d1+d2+d3). Figure (a) shows simulation data and (b) experimental data (see [13] for measurement details). (The gain is shown in linear scale.)